1. Field of the Invention
The invention relates to a method of catalytically decomposing an aqueous hypochlorite solution to oxygen and chloride ion. More specifically, the present invention discloses a method of decomposing aqueous hypochlorite into oxygen and chloride in a solution having a pH value larger than 13, using a catalyst comprising nickel oxide, cobalt oxide or mixtures thereof deposited on an inorganic support, such as magnesium oxide or titanium oxide.
2. Art of Interest
In the decomposition of hypochlorite solutions by solid catalytic means, a continuing problem is encountered when the hypochlorite has a pH of 13 or greater. The usual inorganic catalyst supports disintegrate quickly under these conditions.
In U.S. Pat. No. 4,400,304, R. T. Clark et al. disclose a porous catalyst matrix which is used for the decomposition of aqueous hypochlorite solutions. The catalyst is prepared by sintering a powdered mixture of a particular metal oxide or hydroxide and a thermoplastic polyolefin or halogenated polyolefin.
In U.S. Pat. No. 4,073,873, D. C. Caldwell et al. disclose a process for the catalytic decomposition of hypochlorite by the action of a single-metal spinel of Co.sub.3 O.sub.4, preferably coated on an inert stable support. The Co.sub.3 O.sub.4 catalyst may contain dispersed therein, optionally, the other "modifier" metal oxides which do not affect the single-metal spinel structure of Co.sub.3 O.sub.4, but which contribute better adherence of the Co.sub.3 O.sub.4 to the substrate and improve the toughness of the Co.sub.3 O.sub.4 coating.
In U.S. Pat. No. 3,965,249, D. L. Kinosz discloses the use of an unsupported catalyst to convert hypochlorite to chloride. The decomposition of the hypochlorite occurs at a temperature of between 20.degree. C. and the boiling point of the solution at a pH of between 7-13. The catalyst, selected from salts, fused metal or metal powders of cobalt, nickel, copper or calcium, is converted into a finely divided oxide. This process does not have any organic or inorganic support because the support usually disintegrates at pH values of 10-12. Further, the patent indicates that with certain supports there is no benefit and actually some detriment using zeolite supports.
In U.S. Pat. No. 4,297,333, R. A. Crawford et al. disclose a process for the decomposition of hypochlorite to oxygen and chloride ion in an aqueous solution using a porous solid catalyst of nickel (II) oxide and bimetal NiCo.sub.2 O.sub.4 spinel. The patent does not disclose the decomposition of aqueous hypochlorite solutions having a pH of 13 or higher.
In Water Research, Vol. 9, pp. 1009-1010, Pergamon Press in 1975, V. S. Londbe et al. disclose a catalytic batch process for the controlled decomposition of waste sodium hypochlorite solutions. The catalysts examined were cobalt metal and cobalt acetate without a support at a concentration of about 200 ppm. The process examined the effects of temperature and time.
Based upon this art, it would be extremely useful to have a supported catalyst for the continuous decomposition of hypochlorite in highly alkaline solutions having a pH of 13 or higher. The catalyst support presently used usually decomposes quickly under these high pH conditions. The present invention provides an active catalyst on a inorganic support which is stable in highly alkaline conditions.